Source: CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog#cve20100249
What CISA added#
CISA has listed CVE-2010-0249 in the Known Exploited Vulnerabilities catalog with a remediation due date of June 3, 2026.
The vulnerability affects Microsoft Internet Explorer. CISA describes it as a use-after-free flaw that could allow remote attackers to execute arbitrary code by accessing a pointer tied to a deleted object.
That is the core fact pattern. A memory object is freed. Code later touches a pointer that still refers to it. If an attacker can shape that memory state, the bug may become code execution. CISA’s entry says this vulnerability is known to be exploited.
The affected product is Internet Explorer. CISA also notes that the impacted product could be end-of-life or end-of-service. Its required action is direct: apply vendor mitigations, follow applicable BOD 22-01 guidance for cloud services, or discontinue use if mitigations are unavailable.
This is not a new browser bug in a modern release line. The CVE identifier is from 2010. The reason it matters in 2026 is different: old software has a habit of surviving in places where asset inventories are weakest.
Why an Internet Explorer CVE still matters#
Internet Explorer is not where most users live anymore. That can create the wrong conclusion: that IE risk is gone.
In many environments, the browser itself disappears from daily use before its dependencies disappear from operations. Legacy web apps, old intranet portals, outdated vendor consoles, embedded Windows systems, thin-client workflows, and compatibility modes can keep Internet Explorer-era assumptions alive long after the product stopped being a normal user choice.
That is the practical risk behind an old KEV entry. Attackers do not need a product to be fashionable. They need it to exist, be reachable, and carry a known path to execution.
A use-after-free flaw in a browser-class component is especially relevant because the attack surface often starts with content handling. The source entry does not provide a fresh exploit chain, delivery method, target sector, campaign attribution, or affected deployment details. It only states that the vulnerability is known exploited and describes the code execution condition at a high level.
That uncertainty matters. This should not be read as proof that every modern Windows estate is exposed in the same way. It should be read as a trigger to verify whether Internet Explorer or IE-dependent workflows still exist where they should not.
What not to overclaim#
The CISA entry is concise. It does not say which organizations were targeted. It does not say whether exploitation is ongoing at scale. It does not describe a new exploit. It does not name a threat actor. It does not provide a new Microsoft patch version in the supplied text.
It also does not prove that every system with historical IE components is exploitable. Exposure depends on the actual product state, configuration, mitigations, user workflow, and whether vulnerable code paths are reachable.
The safe reading is narrower and more useful:
- CVE-2010-0249 is in CISA KEV.
- CISA says it is known exploited.
- The affected product is Microsoft Internet Explorer.
- The vulnerability is a use-after-free issue that could allow arbitrary code execution.
- The product may be EoL or EoS.
- Organizations covered by the relevant CISA requirements have a due date of June 3, 2026.
- If mitigations are unavailable, CISA says to discontinue use.
That is enough to justify action without inventing extra drama.
What teams should check now#
The first task is inventory, not panic.
Security teams should confirm whether Internet Explorer is still present, callable, or required anywhere in the environment. That includes standard endpoints, jump boxes, kiosk machines, old Windows Server systems, VDI images, lab systems, OT-adjacent operator stations, and forgotten business units with legacy portals.
The next check is dependency. Some organizations believe they have removed IE because users no longer open it directly. But a business process may still rely on IE mode, old ActiveX-style assumptions, or a legacy application that was never migrated cleanly. Those cases deserve separate treatment. A hidden dependency is harder to retire, but it is still a dependency.
A practical review should cover:
- whether Internet Explorer is installed or enabled anywhere;
- whether users can launch it directly;
- whether any internal app still requires IE behavior;
- whether legacy browser access is allowed from email, chat, or web links;
- whether vulnerable systems can reach untrusted web content;
- whether vendor mitigations exist and are applied;
- whether the affected product is already EoL or EoS;
- whether discontinuing use is the only realistic control.
For federal civilian executive branch agencies, CISA KEV entries carry binding remediation timelines under BOD 22-01. For other organizations, KEV is still useful as a prioritization signal. It tells defenders that the vulnerability has crossed from theoretical risk into exploited reality.
The operational takeaway#
Old browser vulnerabilities are not automatically old risk.
They become current risk when legacy software remains connected to current workflows. Internet Explorer is exactly the kind of product that can survive as an exception: one portal, one vendor app, one business unit, one unmanaged host.
CISA’s required action is blunt for a reason. Apply mitigations if the vendor provides them. Follow the applicable guidance for cloud services. If mitigations are not available, discontinue use.
For this item, the best security move is not to debate whether Internet Explorer should still matter. It is to prove whether it still exists in your environment, then remove the exception or contain it with evidence.
Dead software should not have live attack surface.